My future son-in-law is trying to refinance his home mortgage. The man handling the refinance suggested that he might get a lower interest rate if he included my daughter’s income and assets. They are unmarried, living together in Minnesota and expecting their first child in December. There are two parts to this question: Part One – Is this true about the possible lower interest rate and a good idea? and Part Two – Would they have to file taxes together from that point on? I would appreciate any advice and comments.